Lithium nickel manganese composite oxide, positive electrode active material for lithium secondary battery, lithium secondary battery, and method of producing lithium nickel manganese composite oxide

Abstract

The present invention relates to a lithium nickel manganese composite oxide which includes secondary particles in which a plurality of primary particles are aggregated with each other, and is represented by General Formula (1): Li x Ni y Mn z O 2 (in Formula (1), x is 0.95≤x≤1.1, y is 0.45≤y≤0.5, z is 0.45≤z≤0.5, and y=z is satisfied), wherein Li contained in a transition metal layer does not form LiMn 6 , wherein the lithium nickel manganese composite oxide has a manganese-rich layer from a surface of the secondary particles toward an inside of the secondary particles, wherein a ratio of a number of Mn atoms to a number of Ni atoms (Mn/Ni ratio) in the manganese-rich layer is 1.0 or more and 1.5 or less, and wherein the lithium nickel manganese composite oxide has a space group R-3m, an a-axis lattice constant of 2.87 Å to 2.90 Å, and a c-axis lattice constant of 14.28 Å to 14.32 Å.

What is claimed is: 
     
         1 . A lithium nickel manganese composite oxide which includes secondary particles in which a plurality of primary particles are aggregated with each other, and is represented by General Formula (1): Li x Ni y Mn z O 2  (in Formula (1), x is 0.95≤x≤1.1, y is 0.45≤y≤0.5, z is 0.45≤z≤0.5, and y=z is satisfied),
 wherein Li contained in a transition metal layer does not form LiMn 6 , 
 wherein the lithium nickel manganese composite oxide has a manganese-rich layer from a surface of the secondary particles toward an inside of the secondary particles, 
 wherein a ratio of a number of Mn atoms to a number of Ni atoms (Mn/Ni ratio) in the manganese-rich layer is 1.0 or more and 1.5 or less, and 
 wherein the lithium nickel manganese composite oxide has a space group R-3m, an a-axis lattice constant of 2.87 Å to 2.90 Å, and a c-axis lattice constant of 14.28 Å to 14.32 Å. 
 
     
     
         2 . The lithium nickel manganese composite oxide according to  claim 1 ,
 wherein, in a spectrum measured by solid-state lithium nuclear magnetic resonance analysis ( 6 Li-MAS-NMR) using a magic-angle sample rotation method, there is no peak at 1,495 to 1,505 ppm caused by LiMn 6  formed by Li contained in the transition metal layer.   
     
     
         3 . A positive electrode active material for a lithium secondary battery comprising the lithium nickel manganese composite oxide according to  claim 1  as a main component. 
     
     
         4 . A lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte,
 wherein the positive electrode contains a positive electrode active material whose main component is the lithium nickel manganese composite oxide according to  claim 1 .   
     
     
         5 . A method of producing the lithium nickel manganese composite oxide according to  claim 1 , comprising:
 a first process in which at least one of lithium and a lithium compound is reacted with Ni a Mn b Z a , (Z is O or OH, a is 0<a<1, b is 0<b<1, a+b=1, and α is a value that keeps Ni a Mn b Z a  electrically neutral) to obtain a powder by heating a mixture containing at least one of lithium and the lithium compound, and Ni a Mn b Z a  at 950° C. or higher and 1,150° C. or lower for 1 minute or longer and 5 hours or shorter;   a second process of cooling the powder to room temperature;   a third process in which the powder is immersed in ion-exchanged water at a temperature of 50° C. or higher and 100° C. or lower for 5 minutes or longer and 3 hours or shorter;   a fourth process of drying the powder after being immersed in ion-exchanged water; and   a fifth process in which the powder after drying is heated at 800° C. or higher and 950° C. or lower for 1 hour or longer and 24 hours or shorter.